A collet adaptor is a component of a machine in which a collet is used to clamp a tool or a tool blank for machining. The collet is a clamping device which includes loading and clamping conditions, whereby a tool or tool blank is loaded by insertion into the collet and is thereafter clamped. In the clamping condition, the collet grips the tool or tool blank and with the collet secured within the collet adaptor, the tool or tool blank can be machined, such as by grinding or milling. Collet adaptors secure the collets that clamp the tool.
Collets normally engage a tool or tool blank by gripping a portion of the tool or tool blank, usually one end of the tool or tool blank. In a common form of collet, the gripping section is formed in separated segments, that define a central bore, and that splay outwardly to allow insertion of one end of the tool or tool blank into the bore and which can be closed about the tool or tool blank to grip the tool or tool blank. In many forms of collet adaptor, at least the segmented part of the collet is formed to have a tapered outside surface and the collet adaptor has a complementary tapered bore, so that as the collet is shifted inwardly relative to the collet adaptor, the outside surface of the collet segments slide along the tapered inside surface of the collet adaptor and the segments are slowly pushed radially inwardly to grip the tool or tool blank.
To release the tool or tool blank from the collet, the collet can be shifted forwardly, so that the collet segments splay outwardly and release the gripping load on the tool or tool blank. The tool or tool blank can then be removed from the collet and a new tool or tool blank can be inserted and the process repeated for gripping purposes. All of this process can be automated.
It is important that the mechanism of gripping and release of a tool or tool blank is a simple and quick process. It is also important that the changeover of collets be simple and quick. Combined with these requirements, it is important that the collet adaptor maintain precision grip of a collet and a tool or tool blank.
Collet adaptors with interchangeability capability secure collets in a manner so that different collet sizes can be secured in the same collet adaptor. This differs from collet adaptors which do not have that capability and which are able to secure collets of one size only. Collet adaptors with interchangeability capability typically engage with an elongate drawbar which is external to the collet adaptor and which is part of a tool forming machine (CNC grinding or milling for example). The elongate drawbar connects to one end of a collet adaptor drawbar which itself is connected to the collet. The tool forming machinery often includes an actuator in the form of a piston/pusher rod which connects to the elongate drawbar both of which are associated with or located inside the headstock of the machine and it is the drawbar of the headstock which is connected to the collet adaptor drawbar. In this prior art machinery, the actuator drives the headstock drawbar which drives the collet adaptor drawbar which drives the collet for both clamping and release of tools or tool blanks. Thus the clamping and release mechanisms of the prior art are substantially external to the collet adaptor. Also, in this prior art machinery, the connections are permanent connections, releasable or disengagable only when components are to be replaced or changed or the machinery maintained.
However, in this prior art, alignment errors occur in each connection between and in the prior art, it will be evident that there are multiple connections. A disadvantage of this is that any inaccuracy in alignment of the actuator or elongate drawbar can have an impact on the alignment accuracy of the collet adaptor drawbar and the collet of the collet adaptor, or of the collet adaptor itself.
Also, while mechanical connections between components can introduce alignment errors, other factors such as thermal expansion can also introduce errors and the length and weight of the actuating assembly can magnify these errors. Accordingly, prior art machines are complex in order to compensate for alignment errors of this kind and this elevates the cost of the machinery.
Various prior art forms of collet adaptors exist. These are sometimes complex in terms of the number of parts the collet adaptor comprises, and the manner of operation. Wear of parts can compromise the operation of the collet adaptor, particularly in relation to high precision machining. Complex arrangements are generally more susceptible to wear than arrangements of less complexity. As indicated above, prior art tool forming machinery to which a collet adaptor is connected for use can also embody complex arrangements for shifting the collet within the collet adaptor, and that can also have an adverse effect on the accuracy of the operation of the collet adaptor. It must be appreciated that some uses of the collet adaptor of the invention operate to accuracy at micron level. Thus, any misalignment of the collet within the collet adaptor, or misalignment of the collet adaptor itself, can have an adverse effect on the production of accurate tools.
As indicated, wear of components of a collet adaptor can affect the precision with which a tool or tool blank is machined. Moreover, the environment in which collet adaptors operate makes wear of components highly likely. For example, many of the tools or tool blanks that are gripped by a collet adaptor for machining are formed from carbide, which is an abrasive material and which, during grinding or milling of the tool or tool blank, can form small particles or dust which can enter between components of the collet adaptor. Over time, the carbide can cause wear between the components and when the wear has become sufficient that the precision required of the collet adaptor is no longer available, the collet adaptor must be repaired or replaced.
In addition to the issue of component wear, collet adaptors preferably are easy to operate in terms of connection of collets and connection and release of tools or tool blanks. Some of the more complex prior art collet adaptors are difficult to use and therefore do not satisfy this requirement. Also, the complexity of these arrangements can affect the accuracy of alignment of a tool or tool blank for machining for reasons already explained.
Accordingly, it is an object to provide a collet adaptor which has one or more of a simplified construction, improved accuracy, is easy to use and is less prone to wear. It is further desirable to provide a collet adaptor the operation of which to an operator does not depart significantly from prior art collet adaptors except where the operation is simplified.